One of the most common and life-threatening medical conditions is ventricular fibrillation, a condition where the human heart is unable to pump the volume of blood required by the human body. The usual way of restoring a normal rhythm to a heart experiencing ventricular fibrillation is to apply a strong electric pulse to the heart using an external cardiac defibrillator. External cardiac defibrillators have been successfully used for many years in hospitals by doctors and nurses, and in the field by emergency treatment personnel, e.g., paramedics.
Conventional external cardiac defibrillators first accumulate a high-energy electric charge on an energy storage capacitor. When a series of switching mechanisms are closed, the stored energy is transferred to a patient in the form of a large current pulse. The current pulse is applied to the patient via a pair of electrodes positioned on the patient's chest. A discharge control signal causes the series of switching mechanisms to complete an electrical circuit between the storage capacitor and a wave shaping circuit whose output is connected to the electrodes attached to the patient.
The series of switching mechanisms which couple the energy storage capacitor to the output of the defibrillator may be of different types and configurations. For example, in certain conventional biphasic defibrillators, the series of switching mechanisms may include an output circuit and an isolation relay. The output circuit may consist of a series of solid-state switches in an H-bridge configuration. The isolation relay may be a mechanical relay coupled between the output circuit and the patient, the purpose of which is to ensure that the patient is isolated from the defibrillation circuitry when energy is not being applied to the patient.
Existing self-test methods for defibrillation and pacing circuits verify the integrity of the output circuit while the isolation relay is in a nonconductive state. During these tests, the patient isolation relay is not activated so as to avoid the risk of shock to a patient or bystander. However, this also means that these tests do not verify the integrity of the patient isolation relay. The present invention is directed to a method and apparatus for performing self-tests on defibrillation and pacing circuits, and for verifying the integrity of the patient isolation relay.